1. Field of the Invention
This invention relates to a method for the inhibition of the oxidation of edible oils and for improving the storage stability of oils by dissolving water-soluble natural antioxidants in them.
2. Description of the Prior Art
Oxidative deterioration of products which occurs by the oxidation of the oils and fats contained in these products cannot be prevented by conventional, prior art methods. The oxidative deterioration during the production, process or storage decreases quality and nutritive value of the product. It can also cause other deterioriating effects, such as discoloration, vitamin destruction and polymerization. Therefore, a more effective method for inhibiting oxidation of the products containing oils and fats is necessary.
To overcome this problem, synthetic antioxidants, such as butylated hydroxyanisole, butylated hydroxytoluene, propyl gallate, iso-ascorbic acid, chloro-iso-ascorbic acid, and ascorbyl palmitate have been used. However, there is a tendency for the consumers to prefer natural antioxidants because there is some question as to the safety of the presently used synthetic antioxidants. Although there are various kinds of natural antioxidants, such as tocopherol, plant extracts, gamma-oryzanol and sesamol, few of them are used industrially with satisfaction because of high price, shortage or low antioxidative activity.
Ascorbic acid, Vitamin C, is well known for its physiological effect and widely used as a food additive due to its ability to prevent interacting oxidizable materials with oxygen. It is known that ethylenediaminetetraacetic acid (hereafter abbreviated as EDTA) or disodium ethylenediaminetetraacetic acid (hereafter abbreviated as Na.sub.2 EDTA) prevents oils and fats from being oxidized by inactivating metal ions.
Although ascorbic acid and EDTA (or Na.sub.2 EDTA) can be used as antioxidants in foods, cosmetics or medicines containing a large amount of water because they are easily dissolved in water, they cannot be used in oils and fats, fatty acids and aliphatic acid alkyl esters because of their low solubility in these media. On the other hand, tocopherol is widely used as a supplement to oils and fats for its physiological effect and also used as an antioxidant for its antioxidative activity.